It is well known that when an electrical circuit is broken, there is a tendency for a spark to occur. Many fires have been ignited unintentionally by an electrical spark occurring in an explosive atmosphere. That is, if the atmosphere in the vicinity of the spark should include more than a critical amount of explosive gasses or vapors, an explosion and fire may result and possibly cause extensive damage or loss of life. Accordingly, precautions are customarily taken with electrical circuits in locations where an explosive atmosphere exists, or might exist. A fire, once started, may travel through an electrical conduit, and an explosive atmosphere may enter an electrical conduit and be guided to a switch location. Accordingly, to avoid such transmission through conduits, it has become conventional, under selected circumstances, to provide barriers within the conduit. Examples of structures which provide barriers may be seen in U.S. Pat. Nos. 2,711,438 and 2,835,722, issued June 21, 1955, to C. H. Bissell, and May 20, 1958, to Arthur I. Appleton, respectively. As may be seen in these structures, a special fitting is used to join two sections of conduit, and a sealing compound is placed within a well, or chamber, in the fitting to provide a barrier.
Even in locations which are presumed to be dry it is not uncommon for water to form in the interior of the conduit. This is normally a result of a combination of the changes in atmospheric conditions, humidity, and/or temperature. As a result, outside air is drawn into the conduit system as it "breathes". If such air carries sufficient moisture, it will be condensed within the system when the temperature decreases and chills the air. The resultant water accumulation will remain within the conduit and have more added thereto in response to repeated cycles of the breathing cycle. A collection of such water can adversely affect the electrical circuit, and therefore it has been found desirable to make a provision for draining water, or other liquids, that might otherwise collect in the sealed fitting. A simple opening to effect a drain would, obviously, defeat the purpose of the seal. Suitable drains have been devised which will permit the drainage of liquid from a sealed enclosure without adversely affecting the effectiveness of the seal for preventing the transmission of fire and/or explosive atmospheres. One form of suitable seal is disclosed in U.S. Pat. No. 2,405,927, issued Aug. 13, 1946, to N. A. Tornblom. A wide variety of drains for different types of applications has been developed. The drain, per se, does not form an integral part of this invention, except to the extent that the fitting must allow for the inclusion of one of the variety of drains available. Accordingly, it is believed that the disclosure of the details of any specific drain would only unnecessarily enlarge this specification and obscure the inventive concept.
Typical fittings, of the class described, usually include four ports, two of which are normally aligned and provide means for coupling from the fitting to the conduit. Another port provides a means for connecting a suitable drain plug, and the last port provides a working access for the application of a suitable sealing compound within a well, or chamber, in the fitting. After the application of the sealing compound, a plug closes that access port. In typical prior art structures, care had to be exercised to avoid causing the sealing compound to seal off the drain port. In some structures, a drain port plug was provided and removed after the hardening of the sealing compound. In other structures, a drain port plug and/or core was provided.
In some structures such plug or core was placed or removed through the access or working port and therefore sometimes inconvenienced the artisans working on the fitting and preparing it for receipt of the filling compound. The plug or core also tended to obscure vision, making it difficult to see inside the fitting and determine if the level of the sealing compound in the chamber was at an appropriate level. As a result, it was not unusual to have fittings with either over or underfill.